| 摘要 |
Some embodiments present a method of performing a variable shift operation. This method can be used by a microprocessor that does not allow variable shift operation for certain operand sizes. The method simulates a shift instruction that shifts an operand by a shift count. The method identifies a first shift command and a second shift command. The method computes a mask value. The mask value depends on whether the shift count is less than half of the operand size or greater than or equal to half of the operand size. The method uses the mask value to cause one of the first shift command and the second shift command to produce no shift. In some embodiments, the method allows for the shift count to be specified in bytes or in bits.
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